Silicone fluids applications

Silicone fluids find a very wide variety of applications mainly because of their water-repellency, anti-stick properties, low surface tension and thermal properties. 

Liquid insulators are required for circuit breakers, transformers, and some cable applications. Natural hydrocarbon mineral oils are commonly-used, as well as chlorinated aromatic liquids (desirable because of nonflammability). For high-temperature situations, silicone fluids may be used. Permittivities range between 2 and 7. Insulating liquids function both as electrical insulators and heat-transfer media. See also Dielectric Theory. 

Uses of silicone fluids polish additives, release agents, water-repellent applications, lubricants and greases ... 

Equation (5-44) is applicable to fluids having Prandtl numbers between about 0.6 and 50. It would not apply to fluids with very low Prandtl numbers like liquid metals or to high-Prandtl-number fluids like heavy oils or silicones. For a very wide range of Prandtl numbers, Churchill and Ozoe [9] have correlated a large amount of data to give the following relation for laminar flow on an isothermal flat plate ... 

In recent years one observes a growing industrial demand for organosilicon materials having properties, which can not be found in conventional polymers. These also include silicone fluids, characterized by high refraction indices, such as -1.50, utilized extensively in personal care applications. An important class of such systems are siloxanes having phenylethenyl type substituents along polymer backbone (Fig. 1). 

The amount of catalyst in such cases is rather high 1000-5000 ppm and selectivity towards anti-Markovnikov addition is lower (80-90%), compared to hydrosilylation in the presence of platinum based catalyst. The synthesis of phenylethenyl substituted siloxanes is of commercial importance, driven by potential application in personal care products. Such materials should be in the form of fluids and thus in order to preserve this requirement two approaches have been exploited. One of them involved substitution of less than 100% phenylethenyl moieties, the other made use of 1-hexene as a co-reactant, leading to decreased crystallinity of the final materials. Depending on the structure of (methylhydrido)siloxanes and reaction conditions the resulting silicon fluids exhibited refraction indices ranging from 1.527 to 1.574 (Table 1). 

The linear silicone fluids consists of D units. Silicone elastomers and rubbers are composed of D units bearing as side-chain or end-chain cross-linkable functional groups (vinyl, silanol). Highly branched silicone resins combine T units and D units and in other cases Q and M units. In this way a very great variety of products with a broad application range is obtained. 

Because of the specific hand effects resulting from the use of silicone fluid emulsions, silicones find a wide range of application as softening agents in textile finishing. Application is almost exclusively from the aqueous phase. 

Silicones are well known for their versatility, which makes them ideally suitable for a variety of applications. The fluids can be used as solvents, as foam-control systems, or as release agents (20% of the total volume). High-molecular-weight silicones are mainly used in mbber applications such as High Temperature Vulcanisable (HTV) and Room Temperature Vulcanisable (RTV) (43%), resins (4%), or specialties (15%). Other applications for silicones are masonry protection (8%), textiles (7%), and paper coatings (3%). Silicones can be uniquely tailored for each application area by substitution by reactive groups, allowing them to be cured by different mechanisms. 

Since the principal chemical structures of these new products are almost identical to the already known monofiinctional silicone fluids, the former can be used in all applications already described for the latter, be it in literature, science, or industry. 

We used a new silane which readily permits quantitative conversion of silanol-terminated fluids into aminopropyl-terminated fluids. The reaction between aminopropyl-terminated fluids and diisocyanates proceeds smoothly within a few minutes, either in solution or in the melt. The preparation of siloxane-urea block copolymers is performed in either a two- or a three-component process. By carefully choosing the inorganic segment defined by the corresponding silicone fluid, it is possible to obtain silicone mbbers with different material characteristics. The mechanical properties can be tuned from very soft to very hard. Those materials display tensile strengths up to 14 MPa without requiring additional fillers and can be used for diverse applications. 

An interesting application of the silicone fluids is their coformulation with adhesives to... 

Functional silicones used for release coatings applications are 100% solid silicone fluids. Generally, these polydimethylsiloxane polymers are functionalized by epoxy groups, as shown in Fig. 3. 

In refinery applications such as the delayed coker, linear poly-(dimethylsiloxane)s of intermediate molecular weight are used. These products are normally described in terms of their viscosity in centistokes. Thus a 60,000- or 100,000-centistoke silicone fluid would be the typical recommendation for use in a delayed coker. More viscous and consequently higher molecular weight silicones have been used as described in U.S. Patent 3 700 587 (11). 

Silicone Fluids. Silicone fluids are used in a wide variety of applications, including damping fluids, dielectric fluids, polishes, cosmetic and personal care additives, textile finishes, hydraulic fluids, paint additives, and heat-transfer oils. Polydimethylsiloxane oils are manufactured by the equilibrium polymerization of cyclic or linear dimethylsilicone precursors. Trifunctional organosilane end groups, typically trimethylsilyl (M), are used, and the ratio of end group to chain units (D), ie, M/D, controls the ultimate average molecular weight and viscosity (112). Low viscosity fluids,... 

Silicone fluids have good dielectric properties, loss factor, specific resistance, and dielectric strength at normal operating conditions, and the properties vary only slightly with temperature (59,328,350). The properties in combination with relatively low flammability have led to the use of silicones in transformers and other large electrical applications (351). The dielectric constant of a 1000-cSt oil is 2.8 at 30°C and 2.6 at 100°C. The loss factor is low,... 

RTP produces series of engineering thermoplastics lubricated with PTFE, molybdenum disulfide, graphite powder, silicone and glass, carbon and aramid fibers. Grades AR, TEE and SI include respectively aramid fibers, PTFE (10-20%) and silicone fluid (0.5%). Matrix materials used include PA-6, PA-66, PA-6,10, PA-12, PC, POM, PET, PBT, PSF, PPS, PEI, PEEK and polyphthalamide. The blends have been developed for injection molding of various parts for engineering applications. 

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